The present invention relates to novel fluorobutenes. Furthermore, it relates to a process for producing a fluorobutene by a dehydrofluorination with a raw material of a polyfluorobutane.
Fluorobutenes are useful as monomers for fluorine-containing polymers, synthesized intermediate s/building blocks for producing fluorine-containing intermediates, and raw materials for producing hydrofluorocarbons.
Thermal dehydrofluorination is a well-known process for synthesizing olefins. Dehydrochlorination is widely used for forming a carbon-carbon multiple bond. Furthermore, there are several examples of thermal dehydrochlorination process used for producing fluoroolefins. On the other hand, almost all of thermal dehydrofluorinations are impractical based on a general knowledge due to their low conversion and low selectivity.
As its theoretical background, there is provided that the energy necessary for severing a C—F bond is close to that necessary for severing a carbon-carbon bond since the carbon-fluorine bond is very strong. In general, the temperature necessary for releasing hydrogen fluoride (HF) is far higher than the temperature for dehydrochlorination of an analogous substance containing chlorine atom instead at the defluorination site. Under a high temperature condition necessary for conducting the dehydrofluorination, molecular decomposition reactions and rearrangement reactions compete, thereby lowering selectivity. U.S. Pat. No. 2,480,560 describes that non-catalytic dehydrofluorinations of five different hydrofluorocarbons give fluoroolefins with low selectivity.
Even in the examination process in relation to the present invention of the present inventors, when 1,1,1,4,4,4-hexafluorobutane (HFC-356mf) had been added to a nickel reaction tube at 630° C., it mainly gave trifluoromethane and 3,3,3-trifluoropropene with a conversion of 56%, and it was not possible to obtain 1,1,4,4,4-pentafluoro-1-butene, which is considered to be formed by dehydrofluorination (Comparative Example 1). Furthermore, when 2-trifluoromethyl-1,1,1-trifluoropropane was similarly treated at 660° C., it mainly gave trifluoromethane and 3,3,3-trifluoropropene, and it was not possible to obtain 2-trifluoromethyl-1,1-difluoropropene, which is considered to be formed by dehydrofluorination (Comparative Example 2).
In order to overcome such problems and to efficiently produce fluoroolefins, much effort has been made in the development of catalytic dehydrofluorination. By catalytic process, it may be possible that hydrogen fluoride is released at a temperature lower than that at which the above side reactions become noticeable, thereby causing an expectation for improving selectivity. U.S. Pat. No. 2,599,631 describes both of thermal (non-catalytic) and catalytic processes for producing vinyl fluoride by dehydrofluorination of 1,1-difluoroethane and shows that the catalytic process is more useful. However, one of big problems of the catalytic dehydrofluorination process is a rapid deactivation of the catalyst due to by-products and polymerization products.
Another means for producing fluoroolefins by dehydrofluorination is a process by contact with a base. However, in general, a base-used dehydrofluorination gives in many cases isomers that are different from products obtained by a thermal dehydrofluorination process, and therefore it has been difficult to say that it is an efficient production process of necessary fluoroolefins.